The present invention relates to an optical disk reproducing method and apparatus which are suitable for use with an optical pickup having a first reproduction channel for reproducing recorded information from a first-type optical disk and a second reproduction channel for reproducing recorded information from a second-type optical disk and which provides for high-quality reproduction of recorded information from a third-type optical disk that is reproducible via each of the first and second reproduction channels.
Generally, in DVD (Digital Versatile Disk) players, the optical pickup is equipped with a DVD reproduction channel and CD (Compact Disk) reproduction channel so that DVDs are reproduced via the DVD reproduction channel and CDs are reproduced via the CD reproduction channel.
As optical disks for communication karaoke with background pictures recorded thereon or optical disks for game software, there have been used high-density CDs that are characterized by a higher recording density than that of normal CDs so as to provide a total program-recording time length of 100 min. or over. Information recorded on such high-density CDs can be played back or reproduced by a DVD reproduction channel as well as a CD reproduction channel. Discussion is made below as to which of the DVD and CD reproduction channels can be used more advantageously for reproduction of the high-density CDs. The CD reproduction channel is designed as follows to match physical characteristics of the CD (i.e., normal CD) such as a substrate thickness of 1.2 mm, track pitch of 1.6 xcexcm and linear velocity of 1.2 -1.4 m/sec.
The DVD reproduction channel, on the other hand, is designed as follows to match physical characteristics of the DVD such as a substrate thickness of 0.6 mm, track pitch of 0.74 xcexcm and linear velocity of 3.49 m/sec. in the case of the single-layered DVD.
The high-density CD has physical characteristics somewhat different from those of the normal CD; for example, the high-density CD has a substrate thickness of 1.2 mm, track pitch of 1.3 xcexcm and linear velocity of 0.9 m/sec. If such a high-density CD is reproduced by the CD reproduction channel, high-frequency components (particularly, 3T signals) of reproduced RF signals would be decreased in amplitude, thus deteriorating jitter characteristics. Because such reproduced RF signals can not be put to practical use as they are, it is necessary to amplify each 3T signal by equalizing the signal waveform by use of a transversal filter or the like, in which case, however, noise components would also be amplified to no small degree. But, the CD reproduction channel is advantageous in that it can be more tolerant of (or less susceptible to) a disk""s warp by virtue of its small NA (Numerical Aperture) and is also less susceptible to defects on the disk surface by virtue of its large beam spot diameter. If, on the other hand, the high-density CD is reproduced by the DVD reproduction channel, then there would occur no decrease in the amplitude of the 3T signals; however, the DVD reproduction channel presents the disadvantage that it is susceptible to a disk""s warp due to its large NA and is also susceptible to defects on the disk surface due to its small beam spot diameter.
It is therefore an object of the present invention to provide an optical disk reproducing method and apparatus which are suitable for use in reproduction of recorded information via an optical pickup that includes first and second reproduction channels for reproducing recorded information from first-type and second-type optical disks and is also capable of reproducing recorded information from a third-type optical disk via each of the first and second reproduction channels, just like the one including DVD and CD reproduction channels and capable of reproducing a high-density CD, and which provides for high-quality reproduction of the recorded information from the third-type optical disk.
Warp, surface defects etc. of an optical disk would appear as undesired jitters in RF signals reproduced from the optical disk. Thus, the present invention is characterized by, when reproducing recorded information from a third-type optical disk (other than first-type and second-type optical disks), first test-reproducing the third-type optical disk both via a first reproduction channel and via a second reproduction channel to thereby respectively detect jitter values of the information reproduced via the first and second reproduction channels and then reproducing the recorded information from the third-type optical disk using one of the first and second reproduction channels which attains the jitter value closer to a predetermined target jitter value.
More specifically, the present invention provides an improved optical disk reproducing method which comprises: a step of providing an optical pickup including a first reproduction channel for reproducing recorded information from a first-type optical disk and a second reproduction channel for reproducing recorded information from a second-type optical disk; and a step of, when recorded information is to be reproduced from a third-type optical disk that is different from the first-type optical disk and the second-type optical disk but reproducible via each of the first and second reproduction channels, test-reproducing the recorded information from the third-type optical disk both via the first reproduction channel and via the second reproduction channel to thereby detect a jitter value of the information reproduced via the first reproduction channel and a jitter value of the information reproduced via the second reproduction channel, and then reproducing the recorded information from the third-type optical disk using one of the first and second reproduction channels that attains the jitter value closer to a predetermined target jitter value. Because the above arrangement allows the third-type optical disk to be reproduced via the reproduction channel capable of attaining better jitter characteristics (i.e., jitter value closer to the target jitter value), the present invention always provides for high-quality reproduction of the third-type optical disk irrespective of the condition of the disk.
For example, the first-type optical disk is a DVD and the second-type optical disk is a normal CD, and the first reproduction channel is a DVD reproduction channel and the. second reproduction channel is a CD reproduction channel . Where the third-type optical disk is a high-density CD of the CD recording format which has a higher recording density than that of the normal CD so as to provide a total program-recording time length of 100 min. or over, the third-type optical disk is reproduced via the first or DVD reproduction channel if the better jitter characteristics are attained by the DVD reproduction channel. Similarly, if the better jitter characteristics are attained by the second or CD reproduction channel, then the third-type optical disk is reproduced via the CD reproduction channel. With this arrangement, the present invention always provides for high-quality reproduction of the third-type optical disk irrespective of the condition of the disk.
The present invention also provides an improved optical disk reproducing apparatus which comprises: an optical pickup including a first reproduction channel for reproducing recorded information from a first-type optical disk and a second reproduction channel for reproducing recorded information from a second-type optical disk; a jitter detection section that detects a jitter value of a reproduced RF signal outputted by the first reproduction channel and a jitter value of a reproduced RF signal outputted by the second reproduction channel; and a control section that switches between the first reproduction channel and the second reproduction channel, depending on a type of the optical disk to be reproduced and detected jitter values, in such a manner that the first reproduction channel is used when the recorded information is to be reproduced from the first-type optical disk and the second reproduction channel is used when the recorded information is to be reproduced from the second-type optical disk and also that when recorded information is to be reproduced from a third-type optical disk that is different from the first-type and second-type optical disks but reproducible via each of the first and second reproduction channels, the recorded information is first test-reproduced from the third-type optical disk both via the first reproduction channel and via the second reproduction channel to thereby detect a jitter value of the information reproduced via the first reproduction channel and a jitter value of the information reproduced via the second reproduction channel and then the recorded information is reproduced from the third-type optical disk using one of the first and second reproduction channels that attains the jitter value closer to a predetermined target jitter value.
In a preferred implementation, the optical disk reproducing apparatus further comprises: a waveform equalization section that performs a waveform equalization process on the reproduced RF signals; a waveform-equalization-characteristic adjustment section that adjusts a waveform equalization characteristic of the waveform equalization section, so as to optimize the jitter values detected by the jitter detection section for the reproduced RF signals having been subjected to the waveform equalization process; and a determination section that, when the recorded information is to be reproduced from the third-type optical disk, compares the jitter value of the third-type optical disk test-reproduced using the first reproduction channel and optimized via the waveform-equalization-characteristic adjustment section and the jitter value of the third-type optical disk test-reproduced using the second reproduction channel and optimized via the waveform-equalization-characteristic adjustment section and makes a determination as to which of the first and second reproduction channels attains the jitter value closer to the predetermined target jitter value. In this case, the control section switches the reproduction channel to be used for reproduction of the recorded information from the third-type optical disk, on the basis of a result of the determination.
The optical disk reproducing apparatus may further comprise a disk type identification section that identifies a type of the optical disk having been set in or loaded into the optical disk reproducing apparatus. In this case, the control section controls the switching of the reproduction channel to be used for reproduction of the third-type optical disk, on the basis of the type of the optical disk identified by the disk type identification section.
In the optical disk reproducing apparatus as well, the first-type optical disk optical disk is a DVD and the second-type is a normal CD, and the first reproduction channel is a DVD reproduction channel and the second reproduction channel is a CD reproduction channel. Where the third-type optical disk is a high-density CD of the CD recording format which has a higher recording density than that of the normal CD so as to provide a total program-recording time length of 100 min. or over, the disk type identification section identifies the optical disk as a normal CD if the total program-recording time length represented by the Q subcode information in the lead-in area of the optical disk is less than 100 min., but identifies the optical disk as a high-density CD if the total program-recording time length represented by the Q subcode information in the lead-in area of the optical disk is 100 min. or over.